Sites such as Instagram and YouTube should adopt “zero tolerance” regimes, Simon Stevens said as Unicef data revealed the UK to be among the worst high-income countries for uptake of the jab.

The new data, which tallies children left unvaccinated between 2010 and 2017, follows a steep rise in measles cases in England last year.

The hike is thought to be a direct result of the drop in vaccinations that followed the publication of fraudulent research linking the Measles Mumps and Rubella (MMR) jab to autism by the disgraced British doctor Andrew Wakefield in 1998.

Vaccination coverage among children reaching their second birthday in England is now 91 per cent, with just 87 per cent receiving the second dose by their fifth birthday.

This falls below the 95 per cent coverage experts believe is necessary to achieve “herd-immunity”, where outbreaks are effectively unable to spread.

Symptoms of measles can be sore, red eyes, high temperature and spots on the inside of the cheeks, while serious complications involve pneumonia, fits and diarrhoea.

Mr Stevens described vaccine rejection as a “serious and growing public health timebomb”.

“With measles cases almost quadrupled in England in just one year, it is grossly irresponsible for anybody to spread scare stories about vaccines, and social media firms should have a zero tolerance approach towards this dangerous content,” he said.

Coverage for MMR at two years decreased in 2017-18 for the fourth year in a row, the lowest it has been since 2011-12, which marked the high point of the recovery from the Wakefield scare.

Anti-vax conspiracies have gained traction again in recent years, however, fuelled by social media and endorsement from celebrities such as Jim Carrey and Robert de Niro.

The new Unicef research places Britain third worst among 10 high-income countries for the number of children left unvaccinated, estimated to be 527,000.

Only in the US, where approximately 2,593,000 youngsters are not vaccinated, and France which has 608,000, is the situation worse.

In 2017 there were 259 measles cases in England, rising to 966 in 2018.